De praecipius visus symptomatis eorumque causis Physica & Medica contemplatio

of all the senses previously established by us.

LXIV.
Our opinion is also supported by the pain arising from the sight of luminous things, the cause of which is not a change in the temperament that has happened all at once, but rather the solution of the continuous i.e., the separation of tissue parts because of the turgid humors and spirit from the impulse of light and the distension of the tunics. Furthermore, the three humors lack the sense of touch, and thus they perceive no pain of themselves due to a sudden alteration of temperature.

LXV.
The same reason can be applied to the slaughter of Dionysius, since very dense darkness, kat' antiperistasin by way of opposition/counteraction, forces the spirit of the eyes from the surface into the innermost recesses and strings and condenses the humors more tightly. Whence it happens that, with an abundance of light suddenly supervening, a greater tumult and perversion of the whole instrument arises.

LXVI.
For, by the decree of physicists, the secondary action of extreme contraries, without the progress of a medium, more violently corrupts the nature of the subject because of the doubled cause on both sides. Darkness can blind with the sun, but in a longer time, namely when the light of the spirits is extinguished, the humors and tunics are thickened, and the vivid brightness is obscured, whence there is finally a depraved disposition of the member. Yet, with a gleaming ray suddenly rushing in, it is so far from the position of the parts being restored to wholeness that they are even more and more disturbed by the more valid agitation.

LXVII.
For while the spirit, driven as if to the deepest center, is suddenly cast out by the impression of light